Project Summary The general goal of the proposed research is to understand how cancer associated stroma, including cancer associated fibroblast (CAF), tumor infiltrating lymphocytes (TIL) and their interactions with carcinoma cells contributes to pulmonary metastasis of breast cancer. CAF and TIL are critically involved in mammary tumorigenesis and metastasis. To address the role of CAF and TIL in pulmonary metastasis of mammary cancer, we have established several spontaneous and transplant mammary tumor models. Our research demonstrates that receptor for activated nuclear factor B ligand (RANKL) is expressed by tumor infiltrating CD4+ T cells, mainly Treg cells in tumor associated stroma. RANKL activates its cognate receptor RANK on cell surface of carcinoma cells, which leads to the activation and nuclear translocation of IKK and in turn the repression of maspin, a key metastasis inhibitor in a variety of cancers. However, the links between carcinoma cells, CAF, and CD4+CD25+ T cells still remain obscure. I therefore propose to pursue the following aims: Identify other factors from CAFs responsible for Treg cell infiltration into tumor; Identify signaling pathway that controls chemokine expression from CAF; Examine the role of carcinoma cells in fibroblast activation; Examine the role of alternative NF-B pathways components, including NF-B inducing kinase (NIK), TRAF2, and TRAF3 in ErbB2-induced mammary tumor development and metastasis; and identify upstream members, if other than RANKL that activates NIK/IKK during mammary tumorigenesis. The proposed studies are innovative as they address a poorly explored and controversial research problem with great clinical significance and public health importance.